Award Date

May 2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Committee Member

Ashkan Salamat

Second Committee Member

Keith V. Lawler

Third Committee Member

Joshua Island

Fourth Committee Member

Bernard Zygelman

Fifth Committee Member

MaryKay Orgill

Number of Pages

148

Abstract

The assumptions for the 1912 Grüneisen parameter are reviewed, particularly in the cases of anisotropy, high temperatures, and across phase boundaries. Two main case studies are shown: β-Sn, and Cd. The main techniques of this work involve resistively heated diamond anvil cells with both optical Raman spectroscopy and x-ray diffraction. It is found in Sn that the isothermal mode Grüneisen tensor along increasing isotherms diverges from the single-valued temperature aggregate at the onset of melt, and this is proposed to use as a method of exploring melt phase boundaries in other systems. This method is examined once again on another anisotropic system, Cd, both for its melt and its electronic phase boundaries, which are established here. The lattice dynamic response of body-centered tetragonal β-Sn (I41/amd) under high-pressure and -temperature conditions is determined using experimental optical vibration modes. Raman scattering is used to map the phase stability region of β-Sn to perform mode Grüneisen analysis, and we demonstrate the necessity of an optical intensity calibration for Raman thermometry. The Grüneisen tensor is evaluated along a set of isotherms to address shortcomings of single-mode Grüneisen parameters with respect to anisotropic deformations of this tetragonal structured soft metal. The changes observed here in the Grüneisen tensor as a function of temperature are related to anharmonicity and denote potential criteria for the onset of premelting. Cd’s long-discussed and predicted Electronic Topological Transition (ETT) is observed experimentally and confirmed computationally between 0 and 1GPa. Projections of the excitons onto the electronic density of states calculations show that the change in experimentally observed and theoretically confirmed XAS is due to the ETT, and not due to another structural change (which can also be observed experimentally and explained theoretically). This work establishes a non-structural, purely electronic phase boundary for Cd. Using the phase boundaries laid out in Chapter 3, the isothermal mode Grüneisien tensor, γmj , at temperature for Cd is investigated. Raman and x-ray diffraction data up to 30GPa are collected across five isotherms at 100K intervals from 300-700 K. γmj is found to diverge from the single-valued γ at the onset of melt with increasing isotherms. It is also found that the isothermal mode Grüneisien tensor values are sensitive to subtle electronic changes as shown by aggregations of the data by electronic phase boundary.

Keywords

Cd; Electronic topological transition; Gruneisen tensor; high-pressure; melt criteria; Sn

Disciplines

Condensed Matter Physics | Other Physics | Physics

File Format

pdf

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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